1. Field of the Invention
The present invention relates to a method for optimizing the transmission properties and power loss of a high voltage part, which is integrated in a subscriber line, within a digital telephone exchange wherein telephone signals and data signals are amplified and measured for the purpose of further processing such that, ultimately, the data signals within the high voltage part are transmitted with a high bandwidth substantially without distortions and the power loss of the high voltage part is optimized.
2. Description of the Prior Art
The above-referenced high voltage part is integrated in a subscriber line circuit for connecting a subscriber line in the form of a two-wire copper line. Such a high voltage part is disclosed, by way of example, in the article “A 150 V Subscriber Line Interface Circuit (SLIC) in a new BiCMOS/DMOS—Technology” by Zojer B. et al., Meeting, US, New York, IEEE 1996, pp. 93–96, ISBN: 0-7803-3517-1. On the two-wire copper line leading to the high voltage part, there is transmission of not only telephone signals, which are situated within a frequency band provided for speech, (e.g., telephone signals produced by speech, fax or modem applications), but also data signals (e.g., for multimedia services), whose frequency band is situated above the frequency band provided for speech. In this context, such data signals coming from the subscriber line circuit are transmitted at a high rate (e.g., 1.5 Mbit/s, 2 Mbit/s or 6 Mbit/s) within a broadband transmission channel. Conversely, in the direction toward the subscriber line circuit, such data signals are generally transmitted at a low data rate.
This increase in bandwidth of such subscriber lines in the form of two-wire copper lines is made possible by so-called XDSL technology (Digital Subscriber Line), a new type of transmission method for high-speed data transmission over the customary two-wire copper lines of a telephone network. To prevent analog telephone signals and the XDSL data signals from influencing one another, the latter occupy a frequency band which is situated above the frequency band provided for speech, wherein the frequency band available for XDSL data transmission extends, by way of example, up to 552 kHz or 1.1 MHz.
In the context of setting up Internet access for subscriber terminals belonging to subscribers to the conventional telephone network, XDSL technology is currently becoming increasingly important.
For the XDSL method, the switching side of a subscriber line circuit contains devices for isolating and combining telephone signals and data signals and also devices for a modulation method used in this context (e.g., DMT, CAP, QAM).
Such a subscriber line circuit also integrates a high voltage part in which, in the direction toward the subscriber line circuit, not only the aforementioned conventional telephone signals but also the data signals, which are situated in a frequency band above that provided for speech and which can be transmitted at a high rate using XDSL technology, are amplified and supplied to the subscriber line. In the opposite direction, the telephone signals and the data signals, which are situated in a frequency band above that provided for speech and can be transmitted using XDSL technology, are measured for the purposes of subsequent A/D conversion.
During XDSL data transmission within such a high voltage part, the oscillation curve profile of the analog data signals situated within this high frequency band contains intense nonlinear distortions through the zero point. Above all, These distortions have an adverse effect on the bandwidth and further processing, e.g., in the form of A/D conversion and decoding of the data signals.
In the context of XDSL technology, HDSL technology (high bit rate digital subscriber line) is known, for example. The article “Saving Dynamic Power In HDSL Line Driving Applications” by Nash E., Electronic Design, US, Penton Publishing, Cleveland, Ohio, Vol. 45, No. 12, Jun. 9, 1997 (1997-06-09), pages 88, 90, 92, XP000731500, ISSN: 0013-4872 describes a circuit for an HDSL line driver which is of optimum design in terms of its power loss and distortions in the high bit rate data signals. This article does not explain the extent to which the HDSL line driver is able to satisfy the exchange-side requirements of optimum transmission of pure telephone signals or pure data signals, or the possible simultaneous transmission of telephone signals and data signals.
An object of the present invention is, therefore, to devise a method of the type specified in the precharacterizing clause of patent claim 1 such that the data signals, which are situated above the frequency band provided for speech, are transmitted in a high voltage part with as little distortion as possible and with the highest bandwidth possible, and at the same time the power loss of the high voltage part is optimized.